An electrostatic discharge (ESD) event is a sudden and unexpected voltage and/or current discharge that transfers energy to an electronic device from an outside body (e.g., a human body, which can be approximated in modeling by a human body model ESD events can damage electronic devices, for example by “blowing out” a gate oxide of a transistor in cases of high voltage or by “melting” an active region area of a device in cases of high current, causing junction failure. If devices are damaged by an ESD event, the electronic product can be rendered less operable than desired, or can even be rendered inoperable altogether.
To protect electronic devices from ESD events, engineers have developed ESD protection devices. FIG. 1 shows an example of an integrated circuit 100 that includes an ESD-susceptible circuit 102, having one or more semiconductor devices, which is electrically connected to an exterior circuit assembly (not shown) via an external IC pin 104. The external IC pin 104 can be a supply pin that supplies a DC supply voltage (e.g., VDD or VSS) to the circuit 102, or can be an input/output (I/O) pin that transfers input or output signals there from, for example. A conventional ESD protection device 106 is electrically connected between the circuit 102 and the external IC pin 104 to mitigate damage due to an ESD event 108. If an ESD event 108 occurs, the ESD protection device 106 detects the ESD event 108 and shunts the energy associated with it away from the circuit 102 (e.g., as shown by arrow WESD), thereby preventing damage to the circuit 102. In the absence of an ESD event 108, the ESD protection device 106 is off and thus leaves signals between circuit 102 and pin 104 unchanged.